Canned motors for heating-system circulation pumps can be provided in cylindrical configuration as well as disc rotor and as ball-shaped motor configurations. In these configurations, the stator is mechanically separated and sealed off from the rotor. In the cylindrical design, the mechanical separation and sealing is provided by a metal can. The rotor is cooled within this can by the flow medium (heating water), which also lubricates and damps the bearing.
The production processes used for these configurations of stator and rotor differ in the stator production only insignificantly from processes for making dry-rotor asynchronous motors. The degree of automation is determined here essentially by the configuration of the stator and its characteristic design features such as, for example, by the winding construction.
A hindrance specifically in stator production is that the individual production stations vary greatly in the extent to which the required winding geometry can be automated. In particular, this hinders the fully automatic linking-up of individual production stations within stator production.
The cylindrical stator windings with open and closed cans are likewise in current use. The cylindrical stator windings are in this case arranged so as to be insulated from the metallic can by so-called overhang shields or in taped form by means of necessary air gaps. The pull-in plane of the winding (pull-in-tool) or the position of the coils in the stator space has to be chosen in this case in such a way that the slot space (coil) cannot be fully utilized electrically; the slot utilization is about 50% to 65%.
A further minimization of the motor dimensions while retaining a cylindrical winding, for example with overhang shields or with taping to maintain air gaps with respect to the can, end shield or motor housing comes up against limits or thermal motor loading or of electromagnetic utilization of the machine. The cause is to be seen in the water volume of the canned space or rotor space, which is likewise reduced by the miniaturization, and in the poor slot utilization.
Machines of the rating according to the invention (less than 500 W) and mechanical configuration have their greatest losses in the stator, i.e. so-called Cu losses or ohmic losses. With the previous design principles, the electrical insulation gaps (air or plastic) have a thermally insulting effect in the heat flow to the flow medium.